Apparatus and method for controlling sand moisture

Abstract

An apparatus for controlling the moisture content of sand as it is transported from storage to a mold making apparatus. A conveyor is used to transport a substantially uniform layer of sand at a known rate. The electrical resistance across the sand layer is measured using a series of electrically conductive members that extend into the sand. A thermocouple or other contact device is used to obtain an average temperature of the sand layer. The electrical resistance and average temperature measurements are used in a signal processor to calculate a starting moisture content for the sand. The signal processing unit also calculates an amount of water that should be added to the sand to achieve a computed moisture content value. The signal processing unit further controls the means for adding the water to the sand so that the computed moisture content value is obtained.

I claim: 
     
       1. An apparatus for controlling the moisture content of sand, said apparatus comprising: a conveyor for transporting a substantially uniform layer of sand of a given width;   means for measuring the temperature of said sand layer at at least two points at different depths across the width of said sand layer and generating a temperature signal representing an average of the temperature measured at said at least two points;   at least two parallel, spaced apart electrically conductive members having respective surfaces confronting each other and extending in the direction of sand transport by a distance of about ten inches and being inserted into said sand layer and being located for having at least ten percent of the sand passing by the members at any time located between the respective surfaces;   means for measuring the electrical resistance of the sand between said members and generating a resistance signal representing the electrical resistance of the sand between said members;   means for measuring the transport velocity of the sand layer and generating a velocity signal representing the velocity of the sand layer;   a signal processing unit including signal generating means for generating a predetermined moisture content reference signal and being coupled for receiving said temperature signal, said resistance signal, and said velocity signal, and for calculating a water addition value representing an amount of water addition that will provide the sand in said layer with said predetermined moisture content; and   means for adding water, downstream of the temperature measuring means and said members, to the sand transported in said layer at a rate determined by said water addition value.   
     
     
       2. The apparatus of claim 1 wherein said signal generating means includes operator controllable means for establishing said predetermined moisture content reference signal. 
     
     
       3. The apparatus of claim 1 wherein said electrically conductive members comprise parallel conductive plates that are inserted into the sand layer for at least half the depth of and at transversely spaced locations across the width of the sand layer and are arranged parallel, with respect to the direction of sand transport. 
     
     
       4. The apparatus of claim 1 wherein said conveyor uses a moving belt to transport said sand, said belt having a drive roller and tail roller, and said means for measuring the velocity of the sand layer monitors the angular velocity of said tail roller. 
     
     
       5. The apparatus of claim 1 wherein said means for measuring the temperature of the sand layer comprises a series of three thermocouples positioned at different depths in said sand layer. 
     
     
       6. The apparatus of claim 1 wherein said electrically conductive members are in the form of plates arranged with their width dimension parallel to the direction of sand transport, said plates being spaced apart in a direction transverse to the direction of sand transport and being inserted to a depth in the sand layer such that at least ten percent of the transported sand passing by the plates at any given time is located between the plates. 
     
     
       7. The apparatus of claim 1 where said means for measuring the temperature of said sand layer are spaced apart from said members by a distance, along the direction of sand flow, no greater than the width of said sand layer. 
     
     
       8. A method for controlling the moisture content of sand passing from a supply point to delivery point, said method comprising the steps of: (a) transporting a relatively uniform layer of sand, having a uniform width, from said supply point to said delivery point;   (b) monitoring the transport speed of said sand layer;   (c) measuring the temperature of said sand layer at two or more different locations of differing depths across the width of said layer;   (d) continuously measuring the electrical resistance across at least ten percent of the sand layer located at any given time, within a zone extending approximately ten inches in the direction of sand transport;   (e) establishing a predetermined sand moisture content value;   (f) using the transport speed, sand layer temperature measurements, and electrical resistance measurements to calculate a water addition rate necessary to bring the moisture content of the transported sand to said predetermined sand moisture content value; and   (g) adding water at the calculated addition rate to the sand of said layer at a location downstream, with respect to the direction of sand travel, from the location of sand temperature and electrical resistance measurement.